1. Field of the Invention
The present invention relates to a micromachined capacitive ultrasonic transducer which is manufactured by processing a semiconductor substrate using a micromachining process, a method for manufacturing the ultrasonic transducer, and an ultrasonic endoscope including the ultrasonic transducer in an ultrasonic transmitting and receiving portion.
2. Description of the Related Art
An ultrasonic diagnostic method for applying an ultrasound into a body and visualizing and diagnosing a state in the body from an echo signal of the ultrasound has recently become widespread. Examples of a medical device used for the ultrasonic diagnostic method include an ultrasonic echo device which can visualize a state in a body from a surface of the body and an ultrasonic endoscope which includes an ultrasonic transducer portion for transmitting and receiving an ultrasound at a distal end portion and can be inserted into a body cavity and visualize a state in the body.
Among medical devices for ultrasonic diagnosis, ultrasonic endoscopes are provided with various contrivances for a slimness to improve an ability to be inserted into a body cavity and reduce pain of a patient. For this reason, ultrasonic transducer portions become smaller in size and are provided with various contrivances for a size reduction.
Such a conventional ultrasonic transducer used in an ultrasonic endoscope may contain lead. With recent environmental issues, there is a call for an ultrasonic transducer, provided in an ultrasonic endoscope which is inserted into a body when used, to be lead-free.
It is preferable to use a c-MUT (Capacitive Micromachined Ultrasonic Transducer: including capacitive micromachined ultrasonic probe) as disclosed in, e.g., U.S. Pat. No. 6,836,020 B2 as an ultrasonic transducer whose downsizing can be achieved without using lead.
As another example, an electrostatic type transducer formed on a multi-layered printed circuit board is disclosed in International Publication WO 2003/035281 A2. The electrostatic type transducer has gas pockets serving as air gap portions obtained by forming scratches and pits in an electrode portion. Note that in a technique in International Publication WO 2003/035281 A2, a conductive through hole is formed in a multi-layered rigid substrate or flexible printed circuit board, and a backplate electrode in which gas pockets are formed instead of air gap portions is provided in a roughened backplate.